eMedicine Specialties > Radiology > Cardiac

Cardiomyopathy, Hypertrophic

Diwaker Agarwal, MD, Staff Physician, Department of Radiology, Mercy Medical Center
George Hartnell, MB, Professor of Radiology, Tufts University School of Medicine, Director of Cardiovascular and Interventional Radiology, Department of Radiology, Baystate Medical Center

Updated: Apr 7, 2009

Introduction

Background

Hypertrophic cardiomyopathy (HCM) consists of genetically abnormal, usually hypercontractile and asymmetric myocardium that may obstruct output and cause sudden death if the hypertrophy is localized in the upper septum.

Cardiomyopathy, hypertrophic. Axial electrocardiographically (ECG) gated spin-echo MRI in a patient shows marked septal (S) and less-prominent posterior wall thickening.

Cardiomyopathy, hypertrophic. M-mode echocardiogram recorded at the level of the tips of the mitral valve (horizontal arrows) to assess left ventricular dimensions shows moderate thickening of both the septum (S) and posterior wall of the left ventricle (PW).

Pathophysiology

Hypertrophic cardiomyopathy (HCM) is usually inherited as an autosomal dominant trait involving genes that encode protein constituents of the cardiac sarcomere.² Although 450 different mutations have been identified within 13 genes,³ three genes probably account for more than half of genotyped cases: those that encode beta-myosin heavy chain (chromosome 14), myosin-binding protein C (chromosome 11) and cardiac troponin-T (chromosome 1).²  

On pathologic examination of involved myocardium, the myofibrils are abnormally short, broad, and hypertrophied; in addition, they may run in different directions, with complex intercellular bridging resulting in the formation of whorls.^4,5,6

The left ventricle (LV) is usually more involved in hypertrophy than is the right ventricle. The atria may be dilated, and they are often hypertrophied. The characteristic feature is disproportionate thickening of the interventricular septum (IVS) and the anterolateral wall of the LV compared with the posterior free wall.⁷

Other patterns include concentric hypertrophy; this is sometimes difficult to differentiate from physiologic hypertrophy, which occurs in some highly trained athletes.^8,9 Some patients have significant hypertrophy in unusual locations, such as the posterior portion of the septum, the posterobasal free wall of the LV, or at the midventricular level.⁷ One unusual type involves marked posterior wall hypertrophy and virtually no septal hypertrophy. These patients are young and have severe symptoms.¹⁰

HCM with predominant involvement of apex is especially common in Japan and China. Hypertensive HCM in elderly patients is characterized by severe concentric LV hypertrophy (LVH), a small LV cavity, and hypertension.^11,12 It may look similar to symmetric HCM, but it responds better to beta blockers at doses sufficient to control the hypertension, and patients have a better prognosis.

HCM impairs diastolic relaxation. This impairment in relaxation can result in symptoms of heart failure despite a normal and usually supernormal ejection fraction due to high filling pressures, which result in pulmonary congestion. During systole, approximately 25% of patients have LV outflow obstruction with a dynamic pressure gradient secondary to systolic anterior motion of mitral valve, which further narrows an outflow tract that is already diminished because of septal hypertrophy.

Myocardial ischemia is also common in HCM despite normal epicardial coronary arteries. The causes are multifactorial and include increased muscle mass, inadequate capillary density, elevated diastolic filling pressure, abnormal intramural coronary arteries, impaired vasodilatory reserve, systolic compression of ventricles, and increased myocardial oxygen demand secondary to increased stress.¹

Frequency

United States

Hypertrophic cardiomyopathy is perhaps the most common genetic cardiac disease, with a prevalence of 0.1-0.2% (1 in 500 to 1 in 1000 adults).^7,13 However, the incidence may be higher in select populations.

International

Mortality/Morbidity

The annual mortality among patients with hypertrophic cardiomyopathy (HCM) is approximately 1% when all patients are included, although it is about 3% in large referral centers, which tend to have more severe cases.⁷

• Clinical progression: The clinical course of HCM is variable. In many patients, symptoms are absent or mild. Other patients experience progressive exertional dyspnea, chest pain, and episodes of impaired consciousness, with preserved LV systolic function but diastolic dysfunction.²
• Atrial fibrillation (AF): AF has been reported in 20-25% of HCM patients; chronic atrial fibrillation in particular is associated with substantial morbidity and mortality.^7,17 In general, the rate of clinical deterioration is slow, and symptoms are poorly related to the severity of hypertrophy or the gradient.⁷   however, the prevalence of severe symptoms increases in older patients.¹⁸
• End-stage HCM: In a small minority (5-10%) of patients, HCM progresses to advanced congestive heart failure with LV remodeling and systolic dysfunction.^7,2  Patients with end-stage HCM have an annual mortality of 11% and increased risk of sudden death.¹⁹
• Sudden death: In young persons—young athletes in particular—HCM is the most common cause of sudden cardiac death.^20,21  In children with HCM, the risk of sudden death can be as high as 6% per year.²²  Most sudden deaths are thought to be due to complex ventricular tachyarrhythmias generated by electrically unstable myocardium, with ventricular fibrillation probably being the most common.² Ventricular arrhythmias and inducibility at electrophysiologic testing are less common in children than in older adults, however, which suggests a different mechanism for sudden death in children.²³ Ischemia may play a role in these cases.^24,25

Race

Apical hypertrophic cardiomyopathy is especially common in Japan and China (see also Frequency above). In one study, African Americans accounted for only 8% of all clinically identified HCM patients but for 55% of sudden cardiac deaths among young competitive athletes.²⁶

Sex

Women with hypertrophic cardiomyopathy have been found to be older and more symptomatic than male patients at initial evaluation, more likely to have left ventricular outflow obstruction, and to be at higher risk of progression to advanced heart failure or death.^27,28

Age

Left ventricular hypertrophy (LVH) usually develops in persons 5-15 years of age.²³ Sudden death occurs more commonly in those 12-35 years of age or in those older than 65 years. LVH rarely occurs in children 10 years old or younger.

Presentation

Most patients with hypertrophic cardiomyopathy (HCM) are either asymptomatic or only mildly symptomatic. Such cases are often identified during screening of relatives of known patients with HCM.

Clinical presentation may occur at any age.⁷ Patients may first present with exertional dyspnea, angina, syncope, or atrial fibrillation and systemic embolism. Dyspnea is the most common symptom, occurring in 90% of symptomatic patients.⁷ Angina pectoris occurs in about 75% of symptomatic patients. Fatigue, syncope, and presyncope (graying-out spell) are also common. Sudden death can be the first clinical manifestation; it is common in children and young adults and often occurs during or after physical exertion.²⁹

Most patients with gradients have a double or triple apical impulse, a rapidly rising carotid arterial pulse, and a fourth heart sound.²⁹  A tall A-wave on venous pulsations reflects impaired diastolic relaxation, as does S3 and/or S4. The apical precordial impulse may be shifted laterally, and it is usually forceful and enlarged.

The auscultatory hallmark of HCM is a harsh midsystolic murmur that is best heard between the apex and left sternal border and that commences well after the first heart sound. The murmur becomes louder with a Valsalva maneuver and standing, unlike most other murmurs (except that of mitral valve prolapse). Likewise, vasodilators, dehydration, and inotropes increase the murmur. The potentiated beat after an extra systole also increases the outflow gradient. The murmur often decreases with a hand-grip exercise.

Mitral regurgitation often accompanies HCM, resulting in a holosystolic apical murmur. The murmur of aortic regurgitation occurs in 10% of patients, although Doppler echocardiography shows mild aortic regurgitation in as many as one third of patients.³⁰

Preferred Examination

• Echocardiography: 2-dimensional echocardiography is the usual method of diagnosis.  Echocardiography can be used to confirm the size of the heart, the pattern of ventricular hypertrophy, the contractile function of the heart, and the severity of the outflow gradient. It has the advantages of high resolution and no known risk. Criteria for echocardiographic diagnosis of hypertrophic cardiomyopathy (HCM) have been proposed.³¹ Initial studies of 3-dimensional echocardiography suggest that this technique is superior to 2-dimensional echocardiography for the evaluation of HCM.^32,33
• MRI: The high contrast resolution of ECG-gated MRI provides excellent information about cardiac anatomy. Spin-echo MRI or cine magnetic resonance angiography (MRA) can be used to demonstrate ventricular anatomy and wall thickness. Cine MRA is used to evaluate ventricular function, ventricular end-diastolic and end-systolic volumes, valvular dysfunction, and outflow tract obstruction. In some cases, the signal intensity through the thickened myocardium varies. A major development in MRI is myocardial tagging, which involves localized radiofrequency (RF) saturation of myocardial tissue before image acquisition to permit monitoring of the progressive distortion of the myocardial wall during the cardiac cycle.³⁴ It can provide unique information about regional myocardial strain and function, and it is particularly useful in diseases with regional heterogeneity such as HCM.
• Electrocardiography (ECG): Findings on 12-lead ECG are abnormal in 75-95% of HCM patients.³⁵ Common abnormalities are LVH and widespread, deep, Q waves, which suggest an old myocardial infarction. Many patients have arrhythmias, both atrial and ventricular. ECGs are useful principally for suggesting the possibility of HCM in relatives of HCM patients and in athletes undergoing preparticipation screening.
• Chest radiography: The cardiac silhouette can vary from normal to markedly enlarged in rare cases.
• Thallium-201 myocardial imaging: This test, particularly with single photon emission CT (SPECT) for cross-sectional imaging, can be used to assess myocardial perfusion and the relative thickness of the IVS and free ventricular walls. Gated radionuclide ventriculography permits evaluation of ventricular size, ejection fraction, and septal and wall motion.
• Positron emission tomography (PET): This test can be used as an early diagnostic tool.
• ECG-gated CT: This test can be used to evaluate the patterns of LVH and wall motion in HCM.
• Cardiac catheterization and angiography: These can be performed to evaluate hemodynamic and morphologic abnormalities associated with HCM, along with associated coronary artery anomalies. However, these are invasive procedures and should be used only if other tests cannot provide adequate information or if alcohol ablation of septal branches is planned (see Intervention).
• Electrophysiologic studies (EPS): The role of EPS in identifying HCM patients at risk of sudden death is controversial.⁷ The predictive value of inducible sustained ventricular arrhythmias during EPS is low.²¹
• Magnetic resonance spectroscopy: This is a tool for the evaluation of cardiac metabolism with direct measurement of ischemia-induced changes of high-energy phosphates and intracellular pH.³⁶ The technique is still in the research phase.

Limitations Of Techniques

Echocardiography may at times be limited by poor acoustic windows, incomplete visualization of the left ventricular wall, and inaccurate evaluation of left ventricular mass. Echocardiography is less accurate than MRI in  evaluating wall thickness, especially of the anterolateral LV; it is also less accurate in assessing regional wall motion abnormalities, aneurysms, and delayed enhancement.³⁷

Differential Diagnoses

Amyloidosis, Overview
Aortic Stenosis

Other Problems to Be Considered

Hypertensive heart disease
Subaortic membrane

Radiography

Findings

Chest radiographic findings of hypertrophic cardiomyopathy are variable and nonspecific. The cardiac silhouette can be normal or enlarged. In most cases, cardiomegaly is due to left ventricular hypertrophy and/or left atrial enlargement.⁷ Significant mitral regurgitation leads to left atrial enlargement.

Degree of Confidence

Cardiomegaly is a nonspecific finding on the chest radiographs. The clinical context, however, may suggest HCM as the cause of cardiomegaly.

Computed Tomography

Findings

Electron-beam CT (EBCT) is an excellent method for observing irregular wall hypertrophy, apical morphology, and wall motion dynamics.³⁸ This modality is seldom used, however, because it entails exposure to radiation and contrast medium and provides less information than MRI. The criterion for LV wall hypertrophy is an LV wall thicker than 13 mm. Right ventricular hypertrophy is considered when the right ventricular wall is thicker than 6 mm.

Wall thickening during systole can be calculated with EBCT. Most patients (71%) have decreased wall thickening at the hypertrophic site and normal or increased thickening at the nonhypertrophic site.³⁸ Late enhancement of the myocardium on EBCT has been reported in approximately 47% of HCM patients³⁹ ; this finding suggests the presence of abnormal tissue with a capillary architecture different from that of normal myocardium. The degree of regional wall thickening also is significantly less in areas of late enhancement, which reflects the abnormal myocardial architecture.⁴⁰

Magnetic Resonance Imaging

Findings

Spin-echo MRI and cine MRA

Cardiac morphology can be evaluated by using either ECG-gated spin-echo MRI (see Image 1) or cine MRA (see Image 2). The 2 most common views are 4 chamber (see Images 1-2) and short axis (see Images 3-4).⁴¹

Cardiomyopathy, hypertrophic. Axial electrocardiographically (ECG) gated spin-echo MRI in a patient shows marked septal (S) and less-prominent posterior wall thickening.

Cardiomyopathy, hypertrophic. Oblique axial cine magnetic resonance angiogram in the same patient as in Image above shows a spade-shaped left ventricle with relative sparing of the apical myocardium (arrow).

Cardiomyopathy, hypertrophic. Short-axis cine end-diastolic magnetic resonance angiogram shows asymmetric hypertrophy with septal thickening (S).

Cardiomyopathy, hypertrophic. Short-axis cine end-systolic, magnetic resonance angiogram obtained in the same patient as in Image above shows marked myocardial thickening that affects the entire myocardium.

An obstruction of the LV outflow tract (LVOT) resulting in a subaortic pressure gradient can be detected on cine MRA as signal void (ie, an area of low signal intensity in regions where normal cardiac blood flow produces high signal intensity) (see Image 5). Although areas of physiologic signal void can be seen on scans in healthy individuals, signal voids are larger and persist longer in the cardiac cycle in patients with pathologic conditions that cause obstruction.⁴⁶ Differentiation of physiologic voids from pathologic ones is rarely difficult.

Cardiomyopathy, hypertrophic. Oblique cine magnetic resonance angiogram (outflow 2-chamber view equivalent to a long-axis echocardiogram) shows an area of signal intensity loss (white arrow) in the left ventricular outflow tract, where an obstruction between the hypertrophied septum and anterior mitral leaflet is present. The obstruction is well below the aortic valve ring (between black arrows).

Cardiomyopathy, hypertrophic. Oblique cine magnetic resonance angiogram (outflow 2-chamber view) shows prolapse (arrow) of the posterior mitral leaflet in early systole.

Cardiomyopathy, hypertrophic. Oblique cine magnetic resonance angiogram (outflow 2-chamber view obtained during the same study as Image above) shows mitral prolapse of the posterior mitral leaflet with a small signal intensity loss due to mitral regurgitation (arrow).

Myocardial structural abnormality from fiber disarray and disorganization can result in abnormal signal intensity. Fattori et al reported areas of reduced signal intensity, probably due to myocardial fibrosis, in 16 (43%) of 37 unselected patients with HCM.⁴⁹ This group also had higher maximum septal thickness (25 mm ± 7 vs 21 mm ± 6) and maximum posterior left wall thickness (15 mm ± 9 vs 7 mm ± 8). In patients with HCM, cine MRA also can be used to demonstrate nonuniform regional LV function (ie, LV asynchrony resulting in abnormal diastolic relaxation).

Cardiovascular MRI with gadolinium enhancement can detect myocardial fibrosis.⁵⁰ Gadolinium hyperenhancement may correlate with progressive ventricular dilation and markers of sudden death.⁵¹

Cardiac amyloidosis can resemble HCM; symmetric LV thickening is typical of amyloidosis but also occurs in HCM, and restrictive physiology and poor compliance may be present in both diseases.⁵²  However, amyloidosis tissue may be characterized by its diffuse high signal intensity on T2-weighted spin-echo and short–inversion time inversion recovery (STIR) MRI. The signal intensity with echo times of 20 ms and 60 ms is significantly lower in cardiac amyloidosis than in HCM and in normal tissue.⁵³  Poorer ventricular wall contractility and lower ECG voltages suggest amyloidosis, and a right atrial free wall > 6 mm thick is a specific marker for the disease.⁵³

Magnetic resonance spectroscopy

Contractile dysfunction in HCM is thought to result from alterations in myocardial metabolism. Proton-decoupled phosphorus-31 nuclear magnetic resonance spectroscopy depicts alterations of myocardial metabolism in asymptomatic patients with HCM.⁵⁴ The ratio of phosphocreatine (PCr) to adenosine triphosphate (ATP) is significantly lower in HCM patients than in healthy control subjects.⁵⁴ In addition, patients with severe hypertrophy of the IVS have a significantly increased inorganic phosphate (Pi)–to-PCr ratio compared with that of control subjects.^54,55,45  Both abnormalities are similar to those found in ischemic myocardia. Also, significantly increased phosphomonoester (PME)-to-PCr ratios are present in patients with HCM; this finding indicates altered glucose metabolism.⁵⁴ Myocardial pH is lower in patients with HCM relative to that of control subjects.⁴⁵

MRI myocardial tagging

MRI myocardial tagging can be used to quantify the severity and extent of subtle regional heart wall motion abnormalities. The 3 stages of myocardial tagging are: (1) placement of a saturation band pattern (either a grid or parallel tag lines) over the myocardium with spatially selective RF pulses; (2) MRI acquisition, during which tag motion is observed; and (3) detection of myocardial tag motion.

The motion of the saturation pattern is then used to compute the regional myocardial function. MR tagging techniques offer 2 fundamental improvements over echocardiography and nontagged MRI in regional function assessment: (1) The same volume of myocardium can be tracked throughout the heart cycle to map function in a specific region, and (2) precise quantitative estimates of myocardial shortening and wall thickening can be computed from the images. The position of a myocardial tag can be estimated within approximately 150 µm.

Maier et al found, with myocardial tagging, that the wall motion of the hypertrophied septum was significantly reduced in HCM,⁵⁶ and Kramer et al showed depressed circumferential myocardial segment shortening in the septum and in the anterior and inferior regions.⁵⁷ Three-dimensional analysis of tagged images showed that although circumferential and longitudinal ventricular strains were reduced in patients with HCM, the magnitude of the maximal contraction strain was reduced only in the basal septum and anterior walls.⁵⁸ This finding suggests that a major portion of the mechanical work in HCM contributes to wall shearing and not cavity reduction. Dong et al reported that the myocardium in patients with HCM is heterogeneously thickened and that the fractional thickening and circumferential shortening of the abnormally thickened myocardium are reduced.⁵⁹

Ultrasonography

Findings

Echocardiography

A major criterion for the echocardiographic diagnosis of HCM is LV wall thickness of ³ 13 mm in the anterior septum or posterior wall or ³ 15 mm in the posterior septum or free wall, in the absence of LV dilatation or other cardiac and systemic causes of increased mass.³¹ However, no definitive criterion or single echocardiographic feature is pathognomonic for HCM.

The typical echocardiographic feature in HCM is hypertrophy of the septum and LV anterolateral free wall (see Images 8-9); however, the degree and pattern of hypertrophy vary. Maximum hypertrophy of the septum often occurs midway between the base and the apex. On echocardiograms, asymmetric septal hypertrophy is defined as a ratio of septal thickness to posterior wall thickness of at least 1.3-1.5. Although the average LV wall is thicker than 20 mm (ie, almost twice the normal thickness), it can vary from 13-15 mm in mild hypertrophy to 50 mm in massive hypertrophy.⁸

Cardiomyopathy, hypertrophic. M-mode echocardiogram recorded at the level of the tips of the mitral valve (horizontal arrows) to assess left ventricular dimensions shows moderate thickening of both the septum (S) and posterior wall of the left ventricle (PW).

Cardiomyopathy, hypertrophic. Axial 2-dimensional echocardiogram obtained in the same patient as in Image 8 shows asymmetric septal thickening (23 mm) and a small left ventricular cavity (LV).

Cardiomyopathy, hypertrophic. M-mode echocardiogram recorded at the level of the mitral valve shows a small ventricular cavity (arrow) and systolic anterior motion of the anterior mitral valve leaflet (*).

Cardiomyopathy, hypertrophic. M-mode echocardiogram recorded at the level of the mitral valve in a patient with extreme septal hypertrophy (>40 mm) shows a small ventricular cavity (3 cm) and systolic anterior motion of the anterior mitral valve leaflet (*).

Cardiomyopathy, hypertrophic. M-mode echocardiogram recorded at the level of the aortic valve in the same patient as in Image 8 shows high-frequency flutter on the aortic leaflets (arrows).

Cardiomyopathy, hypertrophic. Continuous-wave Doppler image shows a typical concave profile (arrows) compared with the systolic waveform recorded from the left ventricular outflow; this finding represents subvalvular dynamic outflow obstruction.

Athlete's heart

In the vast majority of competitive athletes, the LV wall is £ 12 mm in thickness. Athletes with an LV wall thicker than 16 mm are likely to have pathologic hypertrophy such as HCM. For the minority of athletes whose LV thickness is in the "gray zone" of 13-15 mm, differentiation of physiologic from pathologic hypertrophy can be problematic. Maron et al published criteria that can help in this distinction.⁸  Echocardiographic features that suggest HCM are an unusual pattern of LVH, asymmetry, end-diastolic LV dimension <45 mm, left atrial enlargement, and abnormal Doppler diastolic indices of LV filling. Other associated features suggestive of HCM are bizarre ECG findings, female sex, and family history of HCM. An end-diastolic LV dimension >55 mm suggests athlete's heart, as does regression of hypertrophy within 3 months after cessation of exercise.⁸

Dilation of the LV chamber

LV chamber dilatation and systolic dysfunction occur in about 1.5% of patients of HCM per year.⁶⁴ This dilatation can evolve into a phase resembling dilated cardiomyopathy.

False Positives/Negatives

Prasad et al have reviewed the pitfalls in the echocardiographic diagnosis of HCM, which include the potential for both false-positive and false-negative readings.⁶⁵

Nuclear Imaging

Findings

²⁰¹ TI myocardial tests

²⁰¹ TI myocardial tests, particularly those with SPECT, permit direct determination of the relative thickness of septum and free wall, and they may be useful in cases in which echocardiography is technically limited. Typically, Tl-enhanced images demonstrate a small LV cavity with marked Tl uptake in the hypertrophied myocardium.

Cardiomyopathy, hypertrophic. Stress (top row) and rest (bottom row) technetium-99m Sesta-2-methoxy-isobutyl-isonitrile (MIBI) perfusion images of hypertrophic cardiomyopathy shows a reversible septal perfusion defect that is not related to coronary obstruction. The septum is markedly thickened (4 cm on the echocardiogram).

Gated radionuclide ventriculography

Gated radionuclide ventriculography with bloodpool labeling permits evaluation of the size and diastolic filling of the ventricular cavity and of the motion of the septum and ventricular wall.

Myocardial scintigraphy

Myocardial scintigraphy with iodine-123– m -iodobenzylguanidine (¹²³ I-MIBG) demonstrates decreased uptake and increased clearance in the hypertrophied myocardium, and it has shown that cardiac sympathetic activity correlates with the degree of hypertrophy function in HCM patients.⁶⁷ Scintigraphy results have proved useful for predicting prognosis in HCM.⁶⁸

Positron emission tomography

In Japanese patients, PET studies performed with¹²³ I-labeled 15-(p -iodophenyl)-3-R,S -methylpentadecanoic acid (BMIPP) suggest that fatty acid metabolism is impaired in areas of myocardium affected by HCM and that BMIPP studies may be useful in classifying HCM and assessing its severity.⁶⁹

Angiography

Cardiomyopathy, hypertrophic. Pressure tracing obtained as the catheter is pulled back from the center of the left ventricle to the aortic root shows a reduction in systolic pressure (arrow 1) in the left ventricle; this finding indicates a subaortic gradient. The waveform changes at the level of the aortic valve, but the systolic pressure does not change (arrow 2). Note the spike-and-dome configuration of the left ventricular pressure tracing.

Cardiomyopathy, hypertrophic. End-diastolic right anterior oblique digital subtraction left ventriculogram shows the normal size and shape of the left ventricle in a patient with hypertrophic cardiomyopathy.

Cardiomyopathy, hypertrophic. End-diastolic right anterior oblique digital subtraction left ventriculogram obtained in the same study as Image above shows a small cavity, with prominent papillary muscles (arrows) projecting into the remains of the ventricular cavity.

Cardiomyopathy, hypertrophic. The 2 images above are used to calculate function and left ventricular dimensions. The outline of the end-diastolic image (Image 16 in Multimedia) has been superimposed on the systolic image (Image 17 in Multimedia). Ejection fractions were calculated by using the area-length method (ejection fraction, 86%) and the Simpson rule (ejection fraction, 84%). The videodensitometric technique shown is inaccurate because of incorrect background registration.

Cardiomyopathy, hypertrophic. Conventional end-diastolic right anterior oblique left ventriculogram acquired during cardiac catheterization shows the normal size and shape of the left ventricle in a patient with hypertrophic cardiomyopathy. Note the distance between the ventricular cavity and the coronary arteries (arrows), which define the epicardial surface of the heart. This distance indicates considerable thickening of the myocardium.

Cardiomyopathy, hypertrophic. Conventional end-systolic right anterior oblique left ventriculogram acquired during the same cardiac catheterization study as in Image above shows a small left-ventricular cavity with mild mitral regurgitation (M). Note the increased distance between the ventricular cavity and the coronary arteries (arrows), which define the epicardial surface of the heart as the myocardium becomes thickened in systole.

Cardiomyopathy, hypertrophic. Conventional right anterior oblique aortogram acquired during cardiac catheterization in the same patient as in Image above shows unobstructed coronary arteries.

Findings

Cardiac catheterization demonstrates decreased LV compliance and, in some patients, a subaortic systolic pressure gradient (see Image 15). The pressure gradient may be labile, varying 0-175 mm Hg in the same patient under different conditions. Increased myocardial contractility can worsen the gradient, particularly in patients with midventricular gradient, because of a direct muscular sphincteric action. Conversely, reduction in contractility or increases in preload or afterload (which increase the LV cavity size) reduce or eliminate the outflow gradient. This dynamic characteristic of HCM distinguishes it from other forms of ventricular outflow obstruction.

The arterial pressure tracing may demonstrate a spike-and-dome configuration (see Image 15). Approximately 25% patients have pulmonary hypertension, at least partly due to decreased LV compliance and elevated left atrial pressure. A right ventricular outflow tract pressure gradient occurs in 15% of patients who have LVOT obstruction, and this likely results from a markedly hypertrophied right ventricle.⁷⁰

Left ventriculography reveals a hypertrophied ventricle with vigorous ejection (see Images 16-20). The papillary muscles often are prominent, filling the LV cavity at the end of systole. In patients with apical involvement, extensive hypertrophy may result in a spadelike configuration of the LV cavity.⁷¹ Associated mitral regurgitation may be present (see Image 18, Image 20). Simultaneous right ventriculography in cranially angulated left anterior oblique projections can be performed for optimal evaluation of the IVS. The left septal surface is flat or it bulges into the LV cavity at its middle or lower portion, in contrast to the normal curve toward the right ventricle.

Coronary angiographic findings usually are normal, but images may show myocardial bridging. The distance between the coronary arteries on the epicardial surface and the ventricular cavity is increased, indicating myocardial hypertrophy (see Images 19-21).

Intervention

The management of hypertrophic cardiomyopathy (HCM) involves identifying and reducing the risk of sudden death and providing medical and/or invasive treatments for the purpose of alleviating symptoms and preventing complications. Family members of patients should undergo echocardiographic screening to facilitate early diagnosis and management.

Determining risk for sudden death

HCM patients should undergo periodic evaluation for risk stratification. These assessments should include the following² :

• Personal and family history
• Two-dimensional echocardiography
• 24- or 48-hour ambulatory ECG monitoring for ventricular tachycardia
• Treadmill or bicycle exercise testing for measurement of blood pressure response.

Electrophysiologic studies are not part of the routine evaluation of HCM patients, but they may be considered in selected cases, such as in patients with otherwise unexplained syncope.

Although the presence of a single marker indicating sufficiently high risk may justify placement of an implantable cardioverter-defibrillator (ICD),⁷² individual risk factors generally have low accuracy for predicting sudden cardiac death in HCM. Consequently, risk factor profiles are often used. Important risk factors include the following²¹ :

• Prior history of cardiac arrest
• History of recurrent syncope and family history of sudden cardiac death
• Severe LVH (maximum wall thickness > 30 mm); positive predictive accuracy for sudden cardiac death 13%, negative predictive accuracy 95%
• LVOT (gradient >30 mm Hg); positive predictive accuracy 7%, negative predictive accuracy 95%
• Stable or decreasing blood pressure in response to exercise; positive predictive accuracy in adults 15%, negative predictive accuracy 97%
• Nonsustained ventricular tachycardia during ambulatory ECG monitoring; in adults, positive predictive accuracy 25%, negative predictive accuracy 85%

Implantable cardioverter-defibrillators

In high-risk HCM patients, ICDs have proved effective and reliable in preventing sudden cardiac death.² An international study of over 500 patients found that the ICDs aborted ventricular tachycardia or fibrillation in 20% of patients; of interventions in patients who received an ICD for primary prevention, 35% were in patients who had undergone implantation for a single risk factor.⁷²

Medical treatment

Pharmacologic therapy is aimed at improving LV diastolic filling, decreasing LVOT obstruction, decreasing myocardial ischemia, and maintaining a sinus rhythm. It should alleviate or reduce the patient's symptoms and improve his or her exercise tolerance.

In patients with LVOT obstruction, beta blockers are the mainstay of medical therapy; disopyramide may be used in combination with beta blockers. In patients with nonobstructive HCM, beta blockers, verapamil, and diltiazem can be used.⁷³  No evidence suggests that the use of beta blockers and verapamil together is more beneficial than the use of either agent alone. Unfortunately, the use of these agents does not prevent sudden death or prolong survival. Verapamil should be used cautiously in patients with marked outflow gradients or elevated pulmonary pressure because its vasodilator effects can result in serious hemodynamic complications. Treatment of end-stage HCM is with diuretics, vasodilators, and digitalis.⁷

Amiodarone can be used in the treatment of both atrial and ventricular arrhythmias. It can provide symptomatic relief, but it has not been shown to prevent sudden cardiac death; ICDs should be used for that purpose. Adverse effects include conduction abnormalities in about 20% of patients. Amiodarone has an American College of Cardiology/American Heart Association/European Society of Cardiology class IIa recommendation (evidence level C) for prevention of recurrent atrial fibrillation in HCM patients.⁷⁴ It should be used only in symptomatic patients and with electrophysiologic guidance.²³

Prophylaxis against infective endocarditis is recommended in HCM with latent or resting LV outflow obstruction or intrinsic mitral valve disease.² Arterial or venous vasodilators may precipitate and aggravate the obstruction and cause hypotension and syncope. Thus, angiotensin-converting enzyme inhibitors and nitrates should be avoided.⁷⁵

Invasive treatment

Invasive treatments are reserved for patients who have severe refractory symptoms despite medical treatment, usually those with outflow tract gradients of 50 mm Hg or more. Approximately 5% of HCM patients overall are candidates for such treatment.² Surgical resection of the hypertrophied IVS (ventricular septal myotomy-myectomy) is the established procedure. The surgical mortality is 2% or less, but the operation should be limited to experienced centers.³⁵  Myectomy has an initial success rate of 90% in decreasing symptoms and LV outflow obstruction, and about 70% of patients maintain improved symptoms and exercise performance for 5 years or longer.^2,7 Complications include left bundle branch block, ventricular septal defect, atrioventricular conduction block, arrhythmias, and aortic regurgitation. Also, the mitral valve with a low-profile prosthetic valve can be replaced to relieve the obstruction.

Dual-chamber pacing has been proposed as a method for decreasing symptoms and improving the hemodynamics in LV outflow obstruction; however, randomized crossover clinical trials have shown little objective evidence of improved exercise capacity.⁷ Pacing is therefore not a primary treatment for HCM, but may be worth considering in selected patients, such as elderly patients of advanced age who are poor surgical candidates.²

Alcohol septal ablation has gained popularity as a treatment for LV outflow obstruction and intractable symptoms refractory to medical or other invasive methods. In this procedure, a small amount of absolute alcohol is injected into the septal branch of the left anterior descending artery supplying the hypertrophied portion of the IVS. This causes a controlled myocardial infarction, reducing obstruction and improving symptoms.

For HCM patients with refractory heart failure, heart transplantation may be the only therapeutic option. Long-term outcome in HCM patients who undergo heart transplantation is comparable to that in patients who undergo transplantation for idiopathic dilated cardiomyopathy.⁷⁶

Medicolegal Pitfalls

Physicians participating in medical evaluations of competitive athletes face potential medicolegal pitfalls, especially in view of the overlap between athlete’s heart and hypertrophic cardiomyopathy.⁷⁷ The American Heart Association (AHA) has published recommendations on preparticipation cardiovascular screening of competitive athletes.⁷⁸ Physicians screening competitive athletes should adhere strictly to these recommendations.⁷⁷

The 36th Bethesda Conference, sponsored by the American College of Cardiology, offered recommendations for monitoring athletes with preclinical HCM, as well as recommending that "Athletes with a probable or unequivocal clinical diagnosis of HCM should be excluded from most competitive sports, with the possible exception of those of low intensity.”⁷⁹

Multimedia

Media file 1: Cardiomyopathy, hypertrophic. Axial electrocardiographically (ECG) gated spin-echo MRI in a patient shows marked septal (S) and less-prominent posterior wall thickening.

Media file 2: Cardiomyopathy, hypertrophic. Oblique axial cine magnetic resonance angiogram in the same patient as in Image above shows a spade-shaped left ventricle with relative sparing of the apical myocardium (arrow).

Media file 3: Cardiomyopathy, hypertrophic. Short-axis cine end-diastolic magnetic resonance angiogram shows asymmetric hypertrophy with septal thickening (S).

Media file 4: Cardiomyopathy, hypertrophic. Short-axis cine end-systolic, magnetic resonance angiogram obtained in the same patient as in Image above shows marked myocardial thickening that affects the entire myocardium.

Media file 5: Cardiomyopathy, hypertrophic. Oblique cine magnetic resonance angiogram (outflow 2-chamber view equivalent to a long-axis echocardiogram) shows an area of signal intensity loss (white arrow) in the left ventricular outflow tract, where an obstruction between the hypertrophied septum and anterior mitral leaflet is present. The obstruction is well below the aortic valve ring (between black arrows).

Media file 6: Cardiomyopathy, hypertrophic. Oblique cine magnetic resonance angiogram (outflow 2-chamber view) shows prolapse (arrow) of the posterior mitral leaflet in early systole.

Media file 7: Cardiomyopathy, hypertrophic. Oblique cine magnetic resonance angiogram (outflow 2-chamber view obtained during the same study as Image above) shows mitral prolapse of the posterior mitral leaflet with a small signal intensity loss due to mitral regurgitation (arrow).

Media file 8: Cardiomyopathy, hypertrophic. M-mode echocardiogram recorded at the level of the tips of the mitral valve (horizontal arrows) to assess left ventricular dimensions shows moderate thickening of both the septum (S) and posterior wall of the left ventricle (PW).

Media file 9: Cardiomyopathy, hypertrophic. Axial 2-dimensional echocardiogram obtained in the same patient as in Image 8 shows asymmetric septal thickening (23 mm) and a small left ventricular cavity (LV).

Media file 10: Cardiomyopathy, hypertrophic. M-mode echocardiogram recorded at the level of the mitral valve shows a small ventricular cavity (arrow) and systolic anterior motion of the anterior mitral valve leaflet (*).

Media file 11: Cardiomyopathy, hypertrophic. M-mode echocardiogram recorded at the level of the mitral valve in a patient with extreme septal hypertrophy (>40 mm) shows a small ventricular cavity (3 cm) and systolic anterior motion of the anterior mitral valve leaflet (*).

Media file 12: Cardiomyopathy, hypertrophic. M-mode echocardiogram recorded at the level of the aortic valve in the same patient as in Image 8 shows high-frequency flutter on the aortic leaflets (arrows).

Media file 13: Cardiomyopathy, hypertrophic. Continuous-wave Doppler image shows a typical concave profile (arrows) compared with the systolic waveform recorded from the left ventricular outflow; this finding represents subvalvular dynamic outflow obstruction.

Media file 14: Cardiomyopathy, hypertrophic. Stress (top row) and rest (bottom row) technetium-99m Sesta-2-methoxy-isobutyl-isonitrile (MIBI) perfusion images of hypertrophic cardiomyopathy shows a reversible septal perfusion defect that is not related to coronary obstruction. The septum is markedly thickened (4 cm on the echocardiogram).

Media file 15: Cardiomyopathy, hypertrophic. Pressure tracing obtained as the catheter is pulled back from the center of the left ventricle to the aortic root shows a reduction in systolic pressure (arrow 1) in the left ventricle; this finding indicates a subaortic gradient. The waveform changes at the level of the aortic valve, but the systolic pressure does not change (arrow 2). Note the spike-and-dome configuration of the left ventricular pressure tracing.

Media file 16: Cardiomyopathy, hypertrophic. End-diastolic right anterior oblique digital subtraction left ventriculogram shows the normal size and shape of the left ventricle in a patient with hypertrophic cardiomyopathy.

Media file 17: Cardiomyopathy, hypertrophic. End-diastolic right anterior oblique digital subtraction left ventriculogram obtained in the same study as Image above shows a small cavity, with prominent papillary muscles (arrows) projecting into the remains of the ventricular cavity.

Media file 18: Cardiomyopathy, hypertrophic. The 2 images above are used to calculate function and left ventricular dimensions. The outline of the end-diastolic image (Image 16 in Multimedia) has been superimposed on the systolic image (Image 17 in Multimedia). Ejection fractions were calculated by using the area-length method (ejection fraction, 86%) and the Simpson rule (ejection fraction, 84%). The videodensitometric technique shown is inaccurate because of incorrect background registration.

Media file 19: Cardiomyopathy, hypertrophic. Conventional end-diastolic right anterior oblique left ventriculogram acquired during cardiac catheterization shows the normal size and shape of the left ventricle in a patient with hypertrophic cardiomyopathy. Note the distance between the ventricular cavity and the coronary arteries (arrows), which define the epicardial surface of the heart. This distance indicates considerable thickening of the myocardium.

Media file 20: Cardiomyopathy, hypertrophic. Conventional end-systolic right anterior oblique left ventriculogram acquired during the same cardiac catheterization study as in Image above shows a small left-ventricular cavity with mild mitral regurgitation (M). Note the increased distance between the ventricular cavity and the coronary arteries (arrows), which define the epicardial surface of the heart as the myocardium becomes thickened in systole.

Media file 21: Cardiomyopathy, hypertrophic. Conventional right anterior oblique aortogram acquired during cardiac catheterization in the same patient as in Image above shows unobstructed coronary arteries.

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Keywords

hypertrophic cardiomyopathy, idiopathic hypertrophic subaortic stenosis, IHSS, asymmetric septal hypertrophy, muscular subaortic stenosis, hypertrophic obstructive cardiomyopathy, HOCM, HCM

Contributor Information and Disclosures

Author

Diwaker Agarwal, MD, Staff Physician, Department of Radiology, Mercy Medical Center
Diwaker Agarwal, MD is a member of the following medical societies: American College of Radiology, American Medical Association, and Radiological Society of North America
Disclosure: Nothing to disclose.

Coauthor(s)

George Hartnell, MB, Professor of Radiology, Tufts University School of Medicine, Director of Cardiovascular and Interventional Radiology, Department of Radiology, Baystate Medical Center
George Hartnell, MB is a member of the following medical societies: American College of Cardiology, American College of Radiology, American Heart Association, Association of University Radiologists, British Institute of Radiology, British Medical Association, Massachusetts Medical Society, Radiological Society of North America, Royal College of Physicians, Royal College of Radiologists, and Society of Cardiovascular and Interventional Radiology
Disclosure: Nothing to disclose.

Medical Editor

Justin D Pearlman, MD, PhD, ME, MA, Director of Advanced Cardiovascular Imaging, Professor of Medicine, Professor of Radiology, Adjunct Professor, Thayer Bioengineering and Computer Science, Dartmouth-Hitchcock Medical Center
Justin D Pearlman, MD, PhD, ME, MA is a member of the following medical societies: American College of Cardiology, American College of Physicians, American Federation for Medical Research, International Society for Magnetic Resonance in Medicine, and Radiological Society of North America
Disclosure: Nothing to disclose.

Pharmacy Editor

Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand
Disclosure: Nothing to disclose.

CME Editor

Robert M Krasny, MD, Consulting Staff, Department of Radiology, Resolution Imaging Medical Corporation
Robert M Krasny, MD is a member of the following medical societies: American Roentgen Ray Society and Radiological Society of North America
Disclosure: Nothing to disclose.

Chief Editor

Eugene C Lin, MD, Consulting Radiologist, Virginia Mason Medical Center; Clinical Assistant Professor of Radiology, University of Washington School of Medicine
Eugene C Lin, MD is a member of the following medical societies: American College of Nuclear Medicine, American College of Radiology, Radiological Society of North America, and Society of Nuclear Medicine
Disclosure: Nothing to disclose.

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